It can happen to you on the Samsung Galaxy S4, that it suddenly receives no GPS signal and therefore your position will not be correctly displayed on the map. Should this be the case also for your Samsung Galaxy S4, then you have the possibility to check the following settings.
Check the following steps to bring the GPS of your smartphone to function again:
1. Is GPS enabled in the location settings of Android? To check this, navigate to: Menu -> Settings -> Tab "Options".
2. Open in this sub-menu "Location". Is this option set to "active"? If yes, then you should have the mode "High accuracy" or "GPS only" enabled. If you have power-saving mode active, GPS is disabled and cannot work well.
Also update the AGPS data of the Samsung Galaxy S4. Instructions, can be found here: How to update A-GPS Data
Then go with your smartphone outside and wait for about 5-15 minutes. Use the app GPS Test to check whether GPS satellites will be found.
If nothing can be found, then you should perform a factory reset and check whether the GPS then works again. If even that does not help, then the GPS module of your Samsung Galaxy S4 is most likely faulty. You should then take the warranty service.